RO134445B1 - Process and plant for gasification of heterogenous mixtures of organic substances and compounds - Google Patents

Description

The present invention relates to a process and an installation for the gasification of heterogeneous mixtures of organic substances and compounds such as biomass waste, forest waste, municipal solid and liquid waste, sludge from sewage treatment plants, etc.

Gasification is a physico-chemical process of irreversible transformation of solid / liquid / gaseous organic compounds into a synthesis gas containing mainly H ₂ , CO and CO ₂ . The physical phenomenon has been known for over 300 years and industrial applications mainly in the fields of energy and petrochemistry have existed for 150 years.

The specialized literature divides the gasification process into 2 distinct stages:

1. The endothermic stage, called pyrolysis.

2. The exothermic stage, called Gasification.

Step 1. Pyrolysis is a process of transformation or thermal decomposition of compounds or organic chemicals under conditions of high temperatures and without oxygen / air. This process involves the simultaneous change of the chemical composition and physical phase of the compound, and is irreversible. In principle, at this stage, due to the temperature, most of the carbon-hydrogen bonds are broken. The result is a gaseous phase consisting of hydrogen and volatile compounds of pyrolysis materials, a liquid phase which is a mixture of hydrocarbons and organic radicals called generically "pyrolysis oil and a solid phase consisting mainly of carbon, mineral residues and metals depending on composition of the original material. The breaking of the carbon-hydrogen bond takes place at a fixed temperature depending on the chemical formula of the organic compound and is a physical characteristic of that compound. The temperature range is 200-1250 ° C, with a high share of pyrolyzed compounds in the range 200-600 ° C.

Step 2. Gasification consists mainly in the transformation of solid carbon into gas by partial oxidation at temperatures above 850 ° C, according to the following exothermic reactions:

C + _^1/2 O ₂ = CO - 123.1 K / kmol carbon

C + O ₂ = CO ₂ - 398.3 Kj / Kmol carbon

The 2 stages take place in a common reactor, in which the thermal energy produced in the exothermic oxidation reactions of carbon is largely consumed for the heating of organic materials in phase 1 of pyrolysis. The resulting singaz contains 5-100 mg / m ³ organic macromolecules with over 100 different chemical formulas, a mixture generically called “tars.

All current patents, academic studies, experimental plants or industrial gasification plants provide for the introduction of the raw material at ambient temperature into the gasification reactor to create a fixed, mobile or fluidized bed. The raw material is passed through the raw material bed, updraft, downdraft or crossdraft, the hot syringe resulting from the exothermic reactions in the gasification area to heat the raw material and bring it to the pyrolysis parameters.

US 006902711 B1 features a process and equipment with industrial application, developed by EBARA Corporation and UBE Industries in Japan. The patent shows a gasification process with a fluidized bed in 2 reactors, the first with temperatures below 800 ° C and the second with temperatures above 1300 ° C.

US 2010/0037519 A1 presents a downdraft gasification process and installation, with fixed bed. To reduce the phenomenon of “channeling the reactor is provided with a central mixer, which leads to increased energy consumption and complicates operation and maintenance.

From a physical point of view, the concept of the current technique provides for the exchange of heat by convection and radiation between a predominantly diatomic gas, which from the point of view of radiation is a transparent body and from the point of view of convection is an insulating material, to a heterogeneous bed. of organic materials which in terms of conduction and convection are insulating materials, with a thermal conductivity coefficient of less than 0,1 W / mK.

EN 134445 Β1 In the inventors' studies and experiments on the gasification of various 1 mixtures of organic materials, they observed a major deficiency in the transfer of heat between the heat transfer agent 3 and the bed of organic matter in the area. of pyrolysis. Naturally, the synthesis gas will move in the mass of the bed of organic material through the free spaces left between the pieces 5 of material, without the possibility for the operator to control anything other than the speed of movement. At the limit, we therefore have a “tube with walls made of organic material with a coefficient of 7 heat transfer through conduction <0.1 W / m-K through which a predominantly biatomic gas moves, with a temperature higher than the walls of the tube. From the point of view of radiation transfer 9, the diatomic gas is a transparent body, so it does not receive and does not give off thermal energy. By convection, the gas will transfer thermal energy to the wall, energy that will accumulate 11 in the surface due to the low conduction coefficient of the walls of organic material. Thus, the organic molecules on the surface will reach the critical temperature of breaking the carbon-hydrogen bond, the hydrogen will be entrained in the gas flow, and the carbon will accumulate on the surface making it even more difficult to transfer heat to the mass of material. These undesirable channeling phenomena are eliminated in the fluidized bed gasification processes, but the heat transfer efficiency is much lower compared to the fixed bed processes due to the high gas velocities 17 imposed by the levitation condition of the fluidized bed. The new "bubbling fluidized bed" processes improve convection heat transfer and bring a small radiation transfer component, but increase energy consumption and greatly complicate the process by introducing and recovering large amounts of quartz sand in the mass. of organic material as a fluidizing agent.

The technical problems solved by the present invention are: 23

- elimination of the phenomena of “channeling in the bed of organic raw material;

- increasing the efficiency of transport and transfer of thermal energy from the exothermic zone 25 to the endothermic zone;

- increasing the efficiency of converting solid carbon into CO and CO ₂ gases with 27 the consequence of reducing residual carbon in slag.

The object of the invention is: 29

- elimination of the bed of organic raw material;

- change of the heat transfer agent as well as of the physical phenomenon 31 used for the transfer of heat energy to the organic raw material;

- controlling the flow of gasifying agent so that in the first phase it creates a vortex flow, and in the second phase it creates a laminar flow with low speed. These two ways of flowing the gasifier will facilitate contact between the gas molecules and the solid carbon atoms.

The present invention consists in a gasification process without a pyrolysis / gas bed which allows the gasification of heterogeneous mixtures of organic materials.

According to fig. 1, the organic feedstock is introduced at ambient temperature into 39 pyrolysis reactors - heading 2 - and is gradually heated to 800 ° C by a metal thermal bridge with the thermal energy produced in the gasification reactor 1. Pyrolysis results, 41 respectively the gaseous, liquid and solid fractions are transferred to the gasification reactor where at temperatures up to 1100 ° C, with air or oxygen gasification agent, there are 43 exothermic reactions of transformation of solid carbon into CO and CO ₂ , gaseous components. The solid fraction remaining in the gasification reactor, which contains mainly molecules and 45 mineral elements from the chemical composition of the chains of organic macromolecules, is separated from the gas fraction and removed by a sluice system consisting of valve 3 and container 4.

RO 134445 Β1

The process according to the present invention consists in transporting the thermal energy from the exothermic gasification zone (fig. 1 position 1) to the endothermic pyrolysis zone (fig. 1 position 2), through the metal thermal bridge formed, according to fig. 4, from the walls of the gasification reactor (position 1 and 12) and the metal enclosure 2 in which the pyrolysis reactor, the flange and the outer walls of the pyrolysis reactor are positioned, respectively positions 1-5 in fig. 2 . From a physical point of view, the heat transfer agent with a thermal conductivity coefficient of 0.02-0.1 W / mK, respectively singas, is replaced by a metal thermal bridge with a conductivity coefficient greater than 45 W / mK, so 400-1000 times higher and in addition with the ability to transfer heat through convection and radiation, not just convection. This new process will significantly increase the efficiency of heat transfer from the exothermic zone to the endothermic zone without additional energy losses and will increase the efficiency of heat transfer to the mass of organic raw material by eliminating the channeling phenomenon. In addition, the thermal bridge formed by the walls of the pyrolysis and gasification reactors will function as a thermal energy accumulator that will deliver energy according to the absorption capacity of the heterogeneous mass of organic materials. In other words, in the current technique, the hot syngas, carrying a quantity of thermal energy, moving towards the outlet of the gasification reactor, passes through the bed of colder organic materials and gives off heat depending on the absorption capacity of the materials encountered during residence. . In the end, the singas leaves the gasifier with the remaining thermal energy. According to the process described in the present invention, the thermal energy is transported through the metal walls of the reactors to the fixed metal surfaces through which the heat is exchanged to the moving organic raw material, thus each piece of organic material, moving through the reactor. pyrolysis, absorbs as much energy as its physical properties allow. This new process of transporting thermal energy, as well as the energy storage property of metal walls, allows the simultaneous treatment of organic materials with different physical properties and implicitly with different water content. Consequently, the raw material no longer has to be dried for homogenization, but can be processed as it is, regardless of the water content. Obviously, materials with a high percentage of water will absorb more energy from the walls and will produce in the gasification reactor an appropriate amount of steam which will correspond in the gasification process with a reduction in the need for steam supplied from outside as a control agent. temperature, so lower processing costs.

The process described in the present invention realizes the controlled transfer of thermal energy by forced convection and by radiation between the metal walls of the reactors and the organic material in controlled motion. According to experimental studies, when moving an organic solid at low speeds in contact with a hot metal wall, after 10 cm the surface of the organic solid is doped with molecular carbon and the heat flux Φ tends to zero. According to this observation, the process according to the present invention provides for the change of the contact surface between the moving material at low speeds and the metal wall at high temperature, after every 10 cm traveled.

Another important experimental observation is that in order to heat 1 Kg of organic mixture from solid urban waste by 700 ° C, a thermal energy of 1600-2200 Kj / Kg is required, depending on the chemical composition and water content of the raw material. This last condition is used to determine the required contact surface and travel speed, depending on the minimum values of the λ / α coefficients of heat transfer by conduction / convection of the organic raw material. The lower the coefficients λ and a, the greater the contact area of the metal-organic material must be increased, keeping the condition that every 10 cm in the direction of movement of the organic material the contact surface changes.

RO 134445 Β1

By changing the heat transfer agent and the absence of the bed of 1 organic material, the gasification process is significantly simplified, which allows an efficient control of the speed of the syngas and implicitly of the residence time to reduce 3 percent of residual carbon left in the slag. Although at temperatures above 900 ° C the oxidation of carbon is instantaneous, in practice a limit of contact time 5 has been observed between solid carbon and gaseous oxygen below which the percentage of residual carbon in slag increases. In other words, although the oxidation is instantaneous, at relatively high rates between the flow of gasifying agent / singase and the solid materials in the gasification reactor, unoxidized carbon remains in the slag. This phenomenon occurs if carbon does not meet with oxygen. It is known that the molar volume of carbon is of the order of 0.00000529 dm ³ / mol and the molar volume of oxygen is of the order of 22.42 dm ³ / mol which means that the distance between 11 2 molecules of oxygen is 4,000,000 times greater than the distance between 2 carbon atoms. Under these conditions, in a laminar flow of oxygen a very low speed is required to obtain random contact only due to the Brownian agitation of the gas. The gasification process according to the present invention (Fig. 4) consists in the chamber 1 wherein the gasifying agent which is mixed by vortex flow, due to the positioning of the nozzles 4, with the solid carbon to facilitate mixing and contact. The steam is preferable to be introduced together with the oxygen, because the water molecules are lighter but larger and the mixture facilitates the vortex flow. From the vortex chamber the non-oxidized solid carbon and mineral materials 19 fall on a rotating grate (fig. 3) where they are in laminar contact with the mixture of singas and oxygen. This zone constitutes the second zone of carbon oxidation under laminar flow conditions 21 at low speed.

To simplify the seals in the area of supply of pyrolysis raw material, the process of pyrolysis and gasification will take place at low pressures in the range of -0.5- ^ 2 bar. The gasifying agent may be air or oxygen, accompanied by steam for temperature control 25 by endothermic reactions. Due to the heterogeneous raw material, the process is controlled by a process software, which allows the real-time adjustment of the process parameters according to 27 state parameters.

The process according to the present invention has very high flexibility with respect to 29 physico-chemical properties of the raw material and allows the processing of virtually any type of organic waste, including but not limited to, agricultural waste, forest waste, 31 municipal waste and the like and sludge from municipal wastewater treatment plants. Given that the process can process heterogeneous organic materials without spilling 33 gases into the environment, this process can be applied to the processing of contaminated organic materials from the category “hazardous without process changes. Also the process 35 can be controlled to obtain the singaz with conditioned composition, starting from an insignificant percentage of CO, which allows to obtain pure technical hydrogen, at different 37 CO / H ₂ ratios for subsequent applications in energy or petrochemistry.

For the application of the presented process and the fulfillment of all the technical conditions, the present invention uses the courts presented in fig. 1 ... 4.

in fig. 1, the cylindrical gasification reactor 1 is shown, detailed in FIG. 3 41 and 4, in which one or more pyrolysis reactors are mechanically fixed (heading 2). Increasing the processing capacity is preferably done by increasing the number of pyrolysis reactors 43 and increasing the size of the gasification reactor. The slag is removed by means of the lock system formed by the valve 3 and the container 4. 45 in fig. 2, the pyrolysis reactor which has a cylindrical shape and is provided with a metal flange 6 for connection to the organic feed system 47 and a metal flange 5 for connection to the corresponding cylindrical enclosure provided in

RO 134445 Β1 gasification reactor fig. 4 position 2). The present invention does not cover the process and the supply installation. Depending on the parameters of the gasification process, a supply equipment in batches with hydraulic piston or a continuous supply system with pressure screw and variable pitch can be used. In both cases, the feeding equipment must be able to control the speed of movement of the organic raw material at the inlet to the pyrolysis reactor in the range of 10-30 mm / s. By means of flange 5, the thermal bridge is made with the cylindrical enclosure that transports the thermal energy from the exothermic area of the gasification reactor (figure 1 position 1) and from the reactor walls to the pyrolysis reactor (fig. 1 position 2). Through the connecting flanges, the thermal energy is transferred by conduction from the gasification reactor to the pyrolysis reactor. in addition, due to its constructive shape, the cylindrical metal enclosure (fig. 4 position 2) with high temperature transmits heat and radiation along its entire length to the pyrolysis reactor (fig. 1 position 2) which due to the continuous inflow of cold raw material, has a lower temperature. For maintenance reasons, the reactor consists of four or more cylindrical sections assembled threaded (Fig. 2 positions 1-4), forming a common body. Each cylindrical section (fig. 2 positions 1-4) contains two groups of metal slats 10 cm high arranged so that the organic raw material, in its movement with a maximum speed of 30 mm / s along the axis of the cylinder (fig. 2 positions 1 -4), to come into contact with the metal slats, each time, on other surfaces of the organic material. For optimal heat transfer through the metal thermal bridge, the slats are welded to the cylindrical body, and for corrosion resistance are made of stainless steel. Due to the fluidization of the displacement of the organic material along the pyrolysis reactor, the distance between the slides is dimensioned so that the minimum passage surface is 2-3 times larger than the maximum size at which the raw material was chopped.

Due to the low heat transfer coefficient, the pyrolysis process of organic materials can be considered a surface process. Theoretically, in order to reduce the residence time and increase the efficiency of heat transfer in the mass of organic material, the solid raw material should be chopped to dimensions comparable to the molecular dimensions. In practice, shredding solid organic materials to sizes smaller than 2-3 cm is uneconomical. This practical reality leads to the lower limitation of the inner diameter of the pyrolysis reactor. The upper limit of the inner diameter is influenced by the dimensions of the gasification reactor. Under these 2 conditions, the inside diameter of the pyrolysis reactor is limited in the range of 200-500 mm, which leads to a processing capacity of 0.8-2.5 t / h. If a higher processing capacity is required, several pyrolysis reactors can be mounted in one gasifier.

The following is a practical installation example for applying the described process.

Example

The pyrolysis reactor shown in FIG. 2 is a reactor with an inside diameter of 240 mm that can process 0.8-1 t / h solid municipal waste from non-hazardous and hazardous categories regardless of the percentage of water contained. The reactor contains 8 sets of metal slats with a height of 10 cm welded to the outer cylindrical wall to take over the thermal energy by conduction and achieve thermal transfer by convection to the organic raw material. The total contact area of the 8 sets of slats amounts to 1.6 m ² . between the sets of blades is a distance of 4 cm for the resettlement and homogenization of the flow of organic material. In their own experiments, moving speeds of organic materials of 10 to 30 mm / s were tested. A relatively uniform temperature distribution was obtained on the contact slats, from 100 ° C at the inlet to the reactor at 800 ° C on the last set of slats, a phenomenon that can be explained due to the supply and distribution system of thermal energy and energy absorbed by matter. organic premium introduced in the process.

RO 134445 Β1

FIG. 3 shows the gasification reactor. 1

The gasification reactor has an original shape, adapted to the process and the new functional conditions, shown in fig. 3, with details of the central part shown in fig. 4. 3

The main differences from the existing installations are:

- the fixed, mobile or fluidized bed of organic raw material characteristic of all 5 gasification installations is missing;

- the raw material processed in the gasification reactor is no longer organic material but 7 solid, liquid and gaseous phases from the pyrolysis reactor;

- in the central part (fig. 4) the vortex enclosure is observed (section “A, position 1) 9 where the gasifying agent (air or oxygen) and steam are introduced by means of a nozzle system (position 4) which creates a vortex current ascending. The steam supply 11 passes through the wall of the vortex chamber for overheating depending on the operating regime of the gasifier. In this way the wall of the vortex chamber also takes over the function of a 13-capacity steam generator with variable capacity, adapted to the steam requirement depending on the chemical composition of the raw material. 15

The rest of the gasifier, the grate (fixed or mobile), the slag evacuation and the singas evacuation are common elements according to the known techniques. The gasification reactor in its entirety is made with the double jacket for water / steam cooling, made of stainless steel without internal thermal insulation. Outside, the reactor is coated with mineral wool thermal insulation 19 to reduce heat loss to the outside.

This gasification reactor with an inner diameter of 2 m, equipped with 2 pyrolysis reactors with an inner diameter of 240 mm, has a processing capacity of approximately 2 t / h mixture of organic materials from non-hazardous and / or hazardous categories, with content 23 water up to 50% mass percentage. Depending on the end use of the synthesis gas, the amount of air and steam can be controlled to obtain an H ₂ / CO ratio between 0.9 and 25 100. The minimum oxidation efficiency of carbon is 90%.

Claims (10)

demand 1. A process for treating heterogeneous mixtures of solid and liquid organic substances and compounds by gasification, characterized in that it comprises the following steps: - the organic raw material in heterogeneous mixture is gradually heated to 900 ... 1000 ° C by convection and thermal radiation, being kept in contact with metal surfaces that transport thermal energy by conduction from the exothermic area of the gasification reactor; - the solid, liquid and gaseous phases resulting from the pyrolysis process are gravitationally transferred to the gasification reactor where they are mixed with the gasifying agent, namely air / oxygen and steam, which are introduced in vortex flow to facilitate contact between the solid / liquid phases, and gaseous; wherein each step has independent control of the process parameters according to the state parameters of the inlet mixture, there is no bed of organic raw material in the process flow and the two process steps are in continuous flow without intermediate accumulation steps. Process according to Claim 1, characterized in that the transport of thermal energy from the exothermic zone to the endothermic zone is carried out by a metal thermal bridge. Process according to Claim 1, characterized in that in the endothermic zone the exchange of thermal energy is carried out by forced convection and radiation between fixed metal walls and a flow of organic materials in a heterogeneous mixture. Process according to Claim 1, characterized in that the heat-transferring metal surfaces are placed in the flow of organic materials in different fixed positions so that the contact surface changes after every 5 to 20 cm. pyrolysis reactor. Process according to Claim 1, characterized in that each group of metal slats inside the pyrolyser forms 2 ... 8 separation planes in the flow of organic raw material, separation planes different from the separation planes of the adjacent blade groups. . Process according to Claim 1, characterized in that, in the gasification step, the oxidation of carbon takes place in 2 different enclosures, in a cascade, the first enclosure with turbulent flow and the second with laminar flow. Plant for the treatment of heterogeneous mixtures of solid and liquid organic substances and compounds by gasification according to the process described in claim 1, characterized in that it consists of: - one or more fixed pyrolysis reactors, positioned in appropriate enclosures created in the gasification reactor, so that by metal-to-metal contact metal thermal bridges are created, which transport the thermal energy from the exothermic zone of the gasification reactor to the endothermic zone of pyrolysis reactor; - a gasification reactor in which the pyrolysis products are gravitationally transferred and processed in two successive chambers, the first with vortex flow and the second with laminar flow of the gasifying agent, respectively air / oxygen and steam. Installation according to Claim 7, characterized in that the cylindrical or prismatic pyrolysis reactor, preferably cylindrical in shape, has 4 ... 14 groups of metal slats with a height of 5 inside positioned transversely by welding to the outer walls. -20 cm, preferably 10 cm, so that the separation planes made by each group are different from the separation plans of the adjacent groups. RO 134445 Β1 Plant according to Claim 7, characterized in that the gasification reactor has no bed of organic raw material. Installation according to Claim 7, characterized in that the gasification reactor 3 contains a nozzle system for introducing air / oxygen and steam so that an upward vortex current is produced in the vortex chamber which will increase the residence time of the products. pyrolysis and will increase the efficiency of carbon oxidation.